For wrapping sheets, brochures and/or folders or bundles of such matter a folded film or sheet, hereinafter called wrapping sheet, is placed around the stack. The purpose of this is to create separate stacks comprising a number of different sheets, brochures and folders, e.g. advertisements which are used for domestic distribution where the wrapping sheet separates the brochures or advertising material which need to be distributed to each household. The task of wrapping the wrapping sheet around the stack may be regarded as relatively simple in that in essence the task is to wrap the sheet around the stack.
This problem may be solved in a purely manual effort in that historically the people distributing such matters prior to distribution assembled the bundles and wrapped the finished stacks by wrapping sheets. However, this process is very slow and very costly. For this purpose a number of automatic devices have been developed.
One example of such a device is applicant's prior patent published in WO 03/008273. This prior art document describes a wrapping apparatus and method where a stack of sheets is conveyed between two superposed conveyors, an upper conveyor and a lower conveyor. The upper conveyor comprises two separate conveyors arranged end to end, with a gap between them. The stack of sheets is placed on a wrapping sheet, which has previously been placed on the lower conveyor, so that the stack approximately cover one third to one half of the sheet and as the stack and wrapping sheet passes the gap between the upper conveyors a number of air nozzles arranged underneath the lower conveyor issues jets so that the wrapping sheet is forced upwards due to the air stream and the wrapping sheet will then engage the second upper conveyor which thereafter will fold the wrapping sheet along the upper side of the stack. In this manner a relatively fast method of wrapping stacks of separate sheets, brochures and or folders is provided.
One drawback, however, with the prior art device and method is the fact that the stack needs to be placed on the first conveyor on top of the wrapping sheet. If the stack is not placed correctly on top of the wrapping sheet, the wrapping induced by the air nozzles may not be correct so that the wrapping sheet is placed in an uneven manner around the stack of sheets, brochures and/or folders. This in turn leads to unevenness when the wrapped stacks are being conveyed on to e.g. a stacker or for manual handling Furthermore, the precise positioning of the stack on top of the wrapping sheet requires that the dispensers or machines further upstream from the wrapping station work in a very precise manner in order to position the stack of sheets, brochures and/or folders correctly on the wrapping sheet. Another drawback is the fact that when it comes to high speed conveying the stack placed on the wrapping sheet may have such a low coefficient of friction between the wrapping sheet and the stack that the acceleration on the conveyors may displace the stack in relation to the wrapping sheet so that an uneven wrapping is the result.
One further example of such a device is described in U.S. Pat. No. 5,009,055. This prior art document describes an apparatus for wrapping a moving bundle of newspapers with a wrapping paper on three sides. The apparatus includes two conveyers for moving the stack to be bundled along a conveying path. The wrapping mechanism is provided for in a gap between the two conveyers, and the wrapping paper is fed from a continuous roll at a predetermined feed rate in a path perpendicular to the conveying path. Means is provided to grip the wrapping material, and to guide the material upwardly so as to cause the wrapping material to wrap itself about the bundle. Means is provided to cut the wrapping material when a predetermined length has been dispensed. The guiding mechanism for gripping the material and feeding it upwardly is driven by a pneumatic cylinder. The rate of movement by the guiding mechanism shall be the same as the paper feed rate, and the operation of the guiding mechanism shall be sequenced according to the location of the stack and paper feed rate.
The method and devise provided for dispensing and positioning the wrapping material is complex and very sensitive to the correct timing of the feed rate and the operation of the pneumatic cylinders. The cylinders are working in a linear translation motion. Each cycle consist of an extraction and retraction of the cylinder. This includes the following detailed steps; acceleration, deceleration, stop, acceleration in reverse direction, deceleration, stop. Each individual step needs to be carefully timed to fit the feed rate of the wrapping material and the bundles. This causes the devise to have a longer set up time. The reliability will be low due to the complexity and parts count, and therefore down time due to maintenance is expected to be high. Furthermore, the productivity of the wrapper is limited, because the pneumatic cylinders are inactive during part of the cycle with respect to wrapping the bundles.
A further example of a device is described in NL 9300006. This prior art document describes an apparatus for wrapping a stack with a wrapping sheet, where the stack comprises one or more substantially superposed sheets, brochures and/or folders wherein a first and second conveyor arranged in line with each other, defining a conveying path, where a gap is present between the first and second conveyor, a wrapping sheet dispenser is superposed the gap, where the wrapping sheet dispenser comprises a rotating waver wheel, such that the waver wheel may position a wrapping sheet in the gap, where said sheets plane is perpendicular to and positioned in the stacks travelling direction. The device makes use of two separate sets of rolls between which the stack is advanced. These separate sets of rollers are a complex device and as mentioned in the above cited prior art this may lead to low reliability.